The present invention relates to an engine intake A/F (air-fuel) ratio control system in an outboard engine system which includes an engine disposed in an engine room defined by an engine support connected to an upper portion of an extension case and by an engine cover covering the engine support, and a catalytic converter incorporated in an exhaust system for the engine, so that an exhaust gas exiting from the exhaust system is discharged under the external water surface via an inside of the extension case, the intake A/F ratio control system being operable to control the air-fuel ratio of an air-fuel mixture to be supplied from a carburetor to the engine.
There is a conventionally known outboard engine system including a catalytic converter incorporated in an exhaust system for an engine, for purifying an exhaust gas (for example, see Japanese Utility Model Publication No.59-18092).
It should be noted here that the catalytic converter exhibits the highest purifying function in an extremely narrow range A of A/F ratio of an exhaust gas around a theoretic A/F ratio (14.6), as shown in FIG. 17. Therefore, when a catalytic converter is used for purifying an exhaust gas from an engine, it is a conventional common practice to detect an A/F ratio of an exhaust gas by an O2 sensor varying an output largely at about a theoretic A/F ratio, and to control the A/F ratio of an air-fuel mixture drawn into the engine, so that the O2 sensor produces an output corresponding to the theoretic A/F ratio, whereby the exhaust gas is always purified with a good efficiency by the catalytic converter.
The O2 sensor varies the output largely relative to a variation in A/F ratio in the range A, but a variation in output relative to a variation in A/F ratio is little produced in a range other than the range A. Therefore, the use of the O2 sensor is advantageous for controlling the A/F ratio of the exhaust gas to the theoretic A/F ratio with a good efficiency, but when the tolerance of the purifying rate of the catalytic converter is set relatively widely with the engine output taken into consideration to a certain extent, it is extremely difficult to carry out the control of the A/F ratio with the O2 sensor.
The present invention has been accomplished with such circumstances in view, and it is an object of the present invention to provide an engine intake A/F ratio control system in an outboard engine system of the above-described type, wherein, in any of a case when the tolerance of the purifying rate of a catalytic converter is set relatively widely with an engine output taken into consideration to a certain extent, irrespective of a narrow range including a theoretic /F ratio, and a case when the set range is shifted to a rich side of the A/F ratio with the engine output taken into serious consideration, the A/F ratio of an exhaust gas can be controlled properly to a desired target value.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an engine intake A/F ratio control system in an outboard engine system which includes an engine disposed in an engine room defined by an engine support connected to an upper portion of an extension case and by an engine cover covering the engine support, and a catalytic converter incorporated in an exhaust system for the engine, wherein an exhaust gas exiting from the exhaust system is discharged under external water surface via an inside of the extension case, characterized in that the engine intake A/F ratio control system comprises a secondary air passage connected to a carburetor provided in an intake system for the engine for supplying secondary air for regulating the A/F ratio of an air-fuel mixture produced in the carburetor; a duty control unit connected to a duty control valve connected to the secondary air passage for controlling the duty ratio of a pulse applied to a coil of the duty control valve; and an LAF sensor (LINEAR AIR-FUEL RATIO SENSOR) mounted to the exhaust system for detecting an A/F ratio of an exhaust gas flowing through the exhaust system, thereby outputting a detection signal proportional to the A/F ratio to the duty control unit.
With the first feature, the A/F ratio of the air-fuel mixture in the carburetor to be supplied to the engine can be controlled in a wide operating range of the engine extending from a low load to a high load by regulating the duty ratio of the pulse applied to the duty control valve by the duty control unit, based on the detection signal of the LAF sensor proportional to the A/F ratio of the exhaust gas, thereby improving the properties of the exhaust gas and enhancing the engine output.
Namely, the output from the LAF sensor is proportional to the A/F ratio of the exhaust gas. Therefore, the A/F ratio of the exhaust gas can be controlled to a narrow range including a theoretic A/F ratio, and also in any of a case when the tolerance of the purifying rate of the catalytic converter is set relatively widely with an engine output taken into consideration to a certain extent, and a case when the set range is shifted to a rich side with the engine output taken into serious consideration, the A/F ratio of the exhaust gas can be controlled properly to a desired target value. Therefore, it is possible to carry out the control operation depending on the operating conditions of the engine such as a mode with the purification taken into serious consideration, a mode with the purification and output taken in consideration and a mode with the output taken into serious consideration. An increase in engine output enables the size of the engine to be reduced and hence, it is easy to place the engine in a narrow engine room in the outboard engine system.
According to a second aspect and feature of the present invention, in addition to the above first feature, a mounting wall is formed in a side wall of an exhaust line integrally connected to the engine to form a portion of the exhaust system, the side wall facing sideways of the outboard engine system, the mounting wall being inclined inwards of the exhaust line toward a lower portion thereof, and the LAF sensor is mounted substantially vertically to the mounting wall.
With the second feature, the mounting wall of the exhaust line is inclined inwards of the exhaust line toward its lower portion. Therefore, the length of protrusion of the LAF sensor mounted substantially vertically to the mounting wall in an outward direction of the outboard engine system can be suppressed to a value as small as possible, whereby the contact of the sensor with another portion or component can be avoided to the utmost, and the detection of the A/F ratio of the exhaust gas can be carried out reliably. Moreover, the LAF sensor is directed outwards of the outboard engine system and hence, it is possible to easily attach and detach the LAF sensor to and from the mounting wall.
According to a third aspect and feature of the present invention, in addition to the second feature, the exhaust line and the mounting wall are formed on the engine support covered with a detachable undercover, and the LAF sensor mounted to the mounting wall is covered with the undercover.
With the third feature, the undercover serves as a protective wall for the LAF sensor, thereby enabling the contact of another portion or component with the sensor to be prevented. In addition, the attachment and detachment of the LAF sensor can be carried out easily in a state in which the undercover has been removed.
According to a fourth aspect and feature of the present invention, there is provided an engine intake A/F ratio control system in an outboard engine system comprising a multi-cylinder engine including a plurality of carburetors for individually supplying an air-fuel mixture into a plurality of cylinders, characterized in that the engine intake A/F ratio control system comprises a single common duty control valve connected to air bleeding chambers in the plurality of carburetors through a dispensing tube, and a duty control unit connected to the duty control valve for controlling the duty ratio of a pulse applied to a coil of the duty control valve.
With the fourth feature, the amount of air mixed into a fuel passed through each of main nozzles of the plurality of carburetors can be controlled by duty-controlling of the pulse applied to the single duty control valve, thereby equally controlling the A/F ratios of the air-fuel mixtures supplied to the plurality of cylinders in the engine, while promoting the atomization of the fuel in the air-fuel mixture.
According to a fifth aspect and feature of the present invention, in addition to the fourth feature, the number of the carburetors is three; three outlet tubes of the dispensing tube made of a hard material are connected to the air-bleeding chambers in the three carburetors; and an air outlet of the duty control valve is connected to a single inlet tube of the dispensing tube, the single inlet tube and the three outlet tubes being disposed so that all of angles formed by the outlet tubes with respect to the inlet tube at connections of these tubes are substantially equal to one another.
With the fifth feature, the resistances in flow paths extending from the single duty control valve to the plurality of carburetors can be equalized, thereby reliably and equally controlling the intake A/F ratios for the plurality of cylinders of the engine.
According to a sixth aspect and feature of the present invention, in addition to the fourth feature, further including an LAF sensor provided in an exhaust passage in the engine for detecting an A/F ratio of an exhaust gas flowing through the exhaust passage to output a detection signal proportional to the A/F ratio, an output portion of the LAF sensor being connected to an input portion of the duty control unit.
With the sixth feature, the intake A/F ratio for each of the cylinders can be controlled in accordance with the A/F ratio of the exhaust gas in a wide operating range of the engine extending from a low load to a high load, thereby improving the properties of the exhaust gas from the engine at all times.
According to a seventh aspect and feature of the present invention, in addition to the fourth feature, the duty control valve includes a valve member accommodated therein and operated to open the duty control valve upon excitation of the coil, the duty control valve being provided with a valve case having an air outlet opened and closed by the valve member, and an outer case surrounding the valve case to define a cylindrical air chamber around the valve case, the valve case being provided with a through-bore which permits an upper portion of the air chamber to communicate with the inside of the valve case, and the outer case being provided with an air inlet which opens a lower portion of the air outlet to the atmosphere.
With the seventh feature, water is sprinkled over the duty control valve from the outside, and even if such water enters the air inlet of the valve, the vigor of the water can be attenuated in the air chamber, whereby the entering of the water into the overlying through-bore and thus into the valve case can be prevented.
According to an eighth aspect and feature of the present invention, in addition to the sixth feature, a catalytic converter is incorporated in the exhaust passage.
With the eighth feature, the properties of the exhaust gas can be improved by the purifying effect of the catalytic converter.
According to a ninth aspect and feature of the present invention, in addition to the sixth feature, a first catalytic converter is mounted in an exhaust collecting chamber communicating with a plurality of exhaust ports in the engine; a second catalytic converter is incorporated in an exhaust passage downstream of the exhaust collecting chamber; and the LAF sensor is provided in an exhaust passage between both of the catalytic converters.
With the ninth feature, the properties of the exhaust gas can be improved at all times in a wide operating range of the engine extending from a low temperature to a high temperature by the purifying effects of the first and second catalytic converters. Moreover, the LAF sensor can be placed easily in the exhaust passage between both of the catalytic converters.
According to a tenth aspect and feature of the present invention, in addition to the fourth feature, an accelerating pump is connected to a flow path connecting each of the air-bleeding chambers in the plurality of carburetors with the single common duty control valve, the accelerating pump pressurizing the flow path in operative association with a rapid opening of a throttle valve in each of the carburetors.
With the tenth feature, the flow path connecting each of the air-bleeding chambers in the plurality of carburetors with the single common duty control valve is utilized for both of control of the amount of air bled and control of the acceleration, and both of the controls can be satisfied by a simple structure.
According to an eleventh aspect and feature of the present invention, there is provided an engine intake A/F ratio control system in an outboard engine system, comprising a secondary air passage connected to a carburetor mounted in an intake system in an engine for supplying secondary air for regulating the A/F ratio of an air-fuel mixture produced in the carburetor, and a duty control valve connected to the secondary air passage to control the amount of secondary air supplied to the carburetor by controlling the duty ratio of a pulse applied to a coil of the duty control valve, characterized in that a surge tank and an orifice are incorporated in series in the secondary air passage.
With the eleventh feature, even if a pressure pulsation is produced in the secondary air passage with the turning-on and off of the pulse applied to the coil of the duty control valve, the pressure pulsation can be attenuated effectively by a damping effect of the surge tank and a constricting resistance of the orifice.
According to a twelfth aspect and feature of the present invention, in addition to the eleventh feature, the secondary air passage is connected to an air-bleeding chamber defined around a main nozzle of the carburetor.
With the twelfth feature, the secondary air supplied from the secondary air passage to the air-bleeding chamber is mixed with a fuel passed through the main nozzle and hence, the regulation of the A/F ratio of an air-fuel mixture and the promotion of the atomization of the fuel can be provided simultaneously.
According to a thirteenth aspect and feature of the present invention, there is provided an engine intake A/F ratio control system in an outboard engine system comprising a multi-cylinder engine disposed in an engine room defined by an engine support connected to an upper portion of an extension case and by an engine cover covering the engine support, with a crankshaft of the engine being turned vertically and a cylinder head of the engine being turned rearwards of a hull, and a plurality of carburetors mounted in a vertical arrangement in the engine for individually supplying an air-fuel mixture to a plurality of cylinders, characterized in that the engine intake A/F ratio control system comprises a single common duty control valve connected to air-bleeding chambers in the plurality of carburetors through a dispensing tube, a duty control unit connected to the duty control valve for controlling the duty ratio of a pulse applied to a coil of the duty control valve, and a surge tank incorporated in a flow path connecting the dispensing tube and the duty control valve to each other.
With the thirteenth feature, the amount of air bled, which is to be mixed with a fuel passed through each of the main nozzles of the plurality of carburetors, can be controlled by duty-controlling the pulse applied to the single duty control valve, thereby equally controlling the intake A/F ratios for the plurality of cylinders in the engine, while improving the atomization of the fuel injected from the main nozzle. Therefore, the only one duty control valve suffices for use, thereby providing a simplification in arrangement, and enabling the engine to be placed easily in the narrow engine room in the outboard engine system, while avoiding the interference with another part or component. Moreover, if a pressure pulsation is produced in a flow path extending from the duty control valve to each of the air-bleeding chambers with the turning-on and off of the pulse applied to the duty control valve, the pressure pulsation can be attenuated effectively by the damping effect of the surge tank.
According to a fourteen aspect and feature of the present invention, in addition to the thirteenth feature, an LAF sensor is provided in an exhaust passage in the engine for detecting an A/F ratio of an exhaust gas flowing through the exhaust passage to output a detection signal proportional to the A/F ratio of the exhaust gas, an output portion of the LAF sensor being connected to an input portion of the duty control unit.
With the fourteenth feature, the intake A/F ratio for each of the cylinders can be controlled in accordance with the A/F ratio of the exhaust gas in a wide operating range of the engine extending from a low load to a high load. Thus, it is possible to improve the properties of the exhaust gas from the engine at all times.
According to a fifteenth aspect and feature of the present invention, in addition to the first feature, the plurality of carburetors are disposed on one of left and right sides of a cylinder block; the surge tank is disposed in one of a first space defined at the rear of the carburetors by a side of the cylinder head and an inner surface of the engine cover and a second space defined by a rear surface of the cylinder head and the inner surface of the engine cover, and a fuel pump is disposed in the other of the first and second spaces and is driven by a valve-operating cam shaft carried in the cylinder head to supply a fuel to each of the carburetors.
With the fifteenth feature, it is possible to carry out the disposition of the fuel pump and the surge tank by effectively utilizing the first space at the rear of the carburetors and the second space at the rear of the cylinder head to contribute to the compactness of the engine room.
According to a sixteenth aspect and feature of the present invention, in addition to the first, eighth or ninth feature, the exhaust system is provided with an exhaust box, an inlet case which is connected to the exhaust system at a location upstream of the exhaust box and opens at a lower end thereof into the exhaust box, and an outlet case which opens at an upper end thereof into the exhaust box above a lower end of the inlet case and also opens at a lower end thereof below the exhaust box; the catalytic converter is mounted in the inlet case; and a drainage pipe bent into an inverted U-shape is mounted to the exhaust box, with one of lower ends of the drainage pipe opening in the proximity to an internal bottom surface of the exhaust box , and the other lower end opening below the exhaust box.
With the sixteenth feature, during operation of the engine, an exhaust pressure of the engine is applied to the inside of the exhaust box to produce a difference in pressure between the inside of the exhaust box and the inside of the extension case. Therefore, when water has been accumulated in the bottom of the exhaust box by any reason, such water is discharged through the drainage pipe into the extension case under the action of the difference in pressure. The bent portion of the drainage pipe is located above both of its lower ends and hence, unless the water level within the extension case is raised, so that the bent portion of the drainage pipe is submerged under the water, the entrance of the water from the drainage pipe into the exhaust box 115 can be prevented. Therefore, it is possible to prevent the entrance of the water into the catalytic converter within the inlet case, thereby prolonging the life of the catalytic converter.
According to a seventeenth aspect and feature of the present invention, in addition to the sixteenth feature, a central bent portion of the drainage pipe is disposed at substantially the same level as of an upper end of the outlet case.
With the seventeenth feature, water-entrance preventing limit water levels in the outlet case and the drainage pipe can be set substantially equivalently, thereby enhancing the function of preventing the entrance of water into the exhaust box.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.